This application claims the benefit of Korean Patent Application No. 2002-6305, filed Feb. 4, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a photoconductive drum in an image forming apparatus, which is adapted for use in an office machine, such as a color copier, color printer and the like, having a plurality of developing devices using electrophotography, and more particularly, to a photoconductive drum in an image forming apparatus and a method of forming the same, the photoconductive drum having an elastic layer formed between a cylindrical base body of the photoconductive drum and a photosensitive layer thereon to protect the cylindrical base body and the photosensitive layer, thereby to maintain a stable image quality and extend a life span of the photoconductive drum.
2. Description of the Related Art
Generally, an electrophotographic image forming apparatus used in an office machine, such as a color copier, color printer and the like, is provided with an organic photoconductive or photosensitive drum 11 which is rotated in one direction by a drum-driving source (not shown), as shown in FIG. 1. Around a circumferential surface of the photoconductive drum 11, a first charging device 12, a laser scanning unit (LSU) 20, four developing devices 31, 32, 33, 34 containing developers of yellow, magenta, cyan, and black, respectively, an image-transferring part 60, an optical discharging or quenching lamp 87, and a cleaning-discharging part 80 are disposed in respective given positions along the rotating direction of the photoconductive drum 11.
The first charging device 12, such as a cyclotron-charging device, electrifies the photoconductive drum 11, and the LSU 20 photo-exposes the photoconductive drum 11 in line shapes along an axial direction thereof through a light source, such as a semiconductor laser source.
Each of the developing devices 31, 32, 33, 34 includes a development roller 13, a developer reservoir 16, a developer-supplying roller 15, a developer layer-regulating member 51 regulating a thickness of a developer layer which is attached on the development roller 13, and a regulating roller 61, 62, 63, or 64 concentrically disposed on both ends of the development roller 13. The components of each developing device 31, 32, 33, or 34 are driven to be rotated by a developing device-driving source (not shown). The developer is supplied to the development roller 13 through the developer-supplying roller 15, and at the development roller 13, regulated in a thin film by the developer layer-regulating member 51. The regulating roller 61, 62, 63, or 64 is disposed to be in contact with the photoconductive drum 11 and to protrude slightly from an outer surface of a developer layer of the development roller 13 such that in a developing process, a given space is formed between the development roller 13 and the photoconductive drum 11.
Also, each of the developing devices 31, 32, 33, 34 is supported to be reciprocally movable by a member (not shown) guiding the developing devices 31, 32, 33, 34. The developing devices 31, 32, 33, 34 are moved toward the photoconductive drum 11 against corresponding releasing springs 74 when eccentric cams 35, 36, 37, 38 rotatably fixed on shafts 56 rotate to push corresponding developing devices 31, 32, 33, 34 toward the photoconductive drum 11. The rotation of shafts 56 is controlled by electronic clutches (not shown). Also, in the developing process, a bias voltage is supplied to the development roller 13. When a negative-positive reversal process is performed in the development roller 13, the bias voltage has the same polarity as the outer surface of the photoconductive drum 11.
The image-transferring part 60 electrostatically transfers a colored visual image formed on the photoconductive drum 11 onto a sheet of printing paper, and the cleaning-discharging part 80 removes the developers remaining on the photoconductive drum 11.
An operation of the image forming apparatus 10 will now be explained.
First, when a printing command is issued, a photoconductive drum 11 is continuously rotated by the drum-driving source, and at the same time, a surface of the photoconductive drum 11 is uniformly electrified by the first charging device 12. When an electrified region (surface) of the photoconductive drum 11 reaches a color developing position, for example, a yellow developing position xe2x80x9cdxe2x80x9d of a yellow developing device 31, an electronic clutch of the yellow developing device 31 is operated to rotate the eccentric cam 36 to move the yellow developing device 31 toward the photoconductive drum 11 in a yellow developing state.
The surface of the photoconductive drum 11 is photo-exposed by the LSU 20 to form an electrostatic latent image of yellow. When the surface of the photoconductive drum 11 is positioned at the yellow developing position xe2x80x9cdxe2x80x9d according to the rotation of the photoconductive drum 11, the electrostatic latent image of yellow is developed from a front end to a rear end thereof to form a continuous yellow image.
After the continuous yellow image is formed and the rear end of thereof is passed through the yellow developing position xe2x80x9cdxe2x80x9d, the eccentric cam 35 is rotated to separate the yellow developing device 31 from the photoconductive drum 11.
After that, when the front end of the yellow image reaches another color position, for example, a magenta developing position xe2x80x9cexe2x80x9d of the magenta developing device 32, an electronic clutch of the magenta developing device 32 is operated to rotate the eccentric cam 36 to move the magenta developing device 32 toward the photoconductive drum 11 in a magenta developing state.
At this time, the yellow image formed on the photoconductive drum 11 is passed by the image-transferring part 60, the quenching lamp 87, and the cleaning-discharging part 80 which are in a non-operating state, and then the front end of the photoconductive drum 11 is disposed again below the first charging device 12. Particularly, the image-transferring part 60 and the cleaning-discharging part 80 are maintained in a non-contact state with the photoconductive drum 11 except in a printing operation so that the yellow image to be passed do not come to be dim or muddy. Below the first charging device 12, the photoconductive drum 11 on which the yellow image is formed is again uniformly electrified and then photo-exposed by the LSU 20 to form an electrostatic latent image of magenta overlappingly on the yellow image.
As the overlappingly formed electrostatic latent image of magenta is positioned at the magenta developing position xe2x80x9cexe2x80x9d according to the rotation of the photoconductive drum 11, it is developed into a continuous yellowxe2x80xa2magenta-overlapped image. After the yellowxe2x80xa2magenta-overlapped image is formed and a rear end thereof is passed through the magenta developing position xe2x80x9cexe2x80x9d, the eccentric cam 36 is rotated and thereby the magenta developing device 32 is separated from the photoconductive drum 11.
Thereafter, when the front end of the yellowxe2x80xa2magenta-overlapped image reaches another color position, for example, a cyan developing position xe2x80x9cfxe2x80x9d of cyan developing device 33, an electronic clutch of the cyan developing device 33 is operated to rotate the eccentric cam 37 to move the cyan developing device 33 toward the photoconductive drum 11 in a cyan developing state.
At this time, the yellowxe2x80xa2magenta-overlapped image formed on the photoconductive drum 11 is positioned again below the first charging device 12 after passing by the image-transferring part 60, the quenching lamp 87, and the cleaning-discharging part 80 which are in the non-operating state. Below the first charging device 12, the photoconductive drum 11 on which the yellowxe2x80xa2magenta-overlapped image is formed is again uniformly electrified and then photo-exposed by the LSU 20 to form an electrostatic latent image of cyan overlappingly on the yellowxe2x80xa2magenta-overlapped image. And, at the cyan developing position xe2x80x9cfxe2x80x9d, the overlappingly formed electronstatic latent image is developed into a continuous yellowxe2x80xa2magentaxe2x80xa2cyan-overlapped image. After the yellowxe2x80xa2magentaxe2x80xa2cyan-overlapped image is formed and the rear end of thereof is passed through the cyan developing position xe2x80x9cfxe2x80x9d, the eccentric cam 37 is rotated to separate the magenta developing device 33 from the photoconductive drum 11.
Next, an electrostatic latent image of black is overlappingly formed and then developed in the same manner as described above, and thereby the entire operation of forming a colored visual image on the photoconductive drum 11 is completed.
Thereafter, the resultant visual image formed on the photoconductive drum 11 is transferred on a sheet of printing paper P fed from a paper-supplying part by the image-transferring part 60.
After transferring, the photoconductive drum 11 is discharged by the quenching lamp 87 and returned to the first state by removing the developers remaining on the surface of the photoconductive drum 11 by a cleaning rotation brush 81 of the cleaning-discharging part 80.
At this time, the printing paper P on which the resultant visual image is transferred is transported to a fusing part to fix the transferred image thereon through a hot roller and then discharged to the outside.
Thus, the conventional image forming apparatus 10 has a structure that the development rollers 13 of four developing devices 31, 32, 33, 34 are operated to come in contact with the photoconductive drum 11 with corresponding developers disposed therebetween to develop corresponding electrostatic latent images. Accordingly, to form the colored visual image, the photoconductive drum 11 performs the developing process once each color, i.e., total 4 times. At this time, the development rollers 13 of the developing device 31, 32, 33, 34 are contacted at a given pressure with or separated from the photoconductive drum 11 by the eccentric cams 35, 36, 37, 38, respectively, so that each of them can be maintained in a development position or a stand-by position.
However, the photoconductive drum 11 is generally formed of a cylindrical member of metal such as aluminum having a high hardness on which a photosensitive layer and the like are coated. Also, the development rollers 13 are formed of cylindrical members of aluminum or a resin having the high hardness. Therefore, contact shocks generated when the photoconductive drum 11 is rotated and comes in contact with the development rollers 13 of the developing devices 31, 32, 33, 34 to perform each developing process are transmitted directly to the entire structure of the photoconductive drum 11, thereby resulting in a non-stabilized image quality developed on the photoconductive drum 11.
Also, impacts caused by changes in pressure generating when the respective development rollers 13 of the developing devices 31, 32, 33, 34 are moved to be in contact with or separated from the photoconductive drum 11 to perform the developing process for each color or to change or replace the developing device 31, 32, 33, or 34, are transmitted directly on the photoconductive drum 11 performing other processes, for example, a charging or photo-exposure process to impair the photosensitive layer of the photosensitive drum 11. As a result, the image quality developed on the photoconductive drum 11 deteriorates or the life span of the photoconductive drum 11 is reduced.
Also, in another conventional image forming apparatus using a contact type charging roller or a contact type transfer roller made of a rigid body, the contact shocks generated when the photoconductive drum is rotated and comes in contact with the contact type charging roller or the contact type transfer roller to perform the charging or transferring process, are transmitted directly on the photoconductive drum. As a result, the image quality developed on or transferred by the photoconductive drum is destabilized.
Therefore, it is an object of the present invention to provide an improved photoconductive drum and image forming apparatus using the same, which has an elastic layer formed between a cylindrical base body of the photoconductive drum and a photosensitive layer thereon to absorb shocks generating when the photoconductive drum comes in contact with a development roller of a high hardness and impacts caused by the development roller when developing devices are exchanged or replaced, thereby protecting the cylindrical base body and the photosensitive layer to maintain a stable image quality and to extend a life span of the photoconductive drum.
It is another object to provide an improved photoconductive drum and image forming apparatus using the same, which can absorb shocks generating when the photoconductive drum comes in contact with a development roller, a charging roller, and a transfer roller, and impacts caused by the development roller when developing devices are exchanged and replaced, to protect a photosensitive layer of the photoconductive drum, thereby to maintain a stable image quality and to extend a life span, even though the charging roller or the transfer roller as well as the development roller is formed of a rigid body.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
These and other objects may be achieved, according to an embodiment of the present invention, by providing a photoconductive drum forming an image by using an electric potential characteristic of a surface thereof. The photoconductive drum includes a cylindrical member, a photosensitive layer formed on the cylindrical member to be chargeable with electricity, and an elastic layer formed in a thickness greater than 10 xcexcm between the cylindrical member and the photosensitive layer.
A hardness of the elastic layer measured by the Asker xe2x80x9cCxe2x80x9d scale is below 70 degrees.
The cylindrical member is made of a conductive material of one of a metal, such as copper, aluminum, gold, argentum, platinum, palladium, iron, nickel, stainless steel and the like, and an alloy containing the metal as a major ingredient. The cylindrical member may have a film made of one of aluminum, aluminum-contained alloy, and indium tin oxide (ITO)-contained alloy and formed on the conductive material by a vacuum plating or evaporation (sputtering) method.
Alternatively, the cylindrical member can be formed of a plastic material impregnated by fine conductive particles together with plastic having a predetermined binder or a conductive binder. In this case, the plastic material is made of thermo-plastic resin of at least one selected from a group consisting of polycarbonate resin, acryl resin, styrene resin, polyolefin resin, fluoric resin, polyester resin, polyphenylene-sulfide resin, polyphthalamide resin, and liquid crystal polymer; a conductive agent controlling an electric resistance and made of a conductive material of at least one selected from a group consisting of carbon black, tin oxide, titanium oxide, and argentum; and a dispersing agent made of an inorganic material, such as calcium carbonate and clay, to uniformly disperse the conductive agent.
The elastic layer is made of a material of at least one selected from a group consisting of elastomers such as butyl rubber, fluoric rubber, acryl rubber, ethylene-propylene-diene-methylene (EPDM) rubber, acrylonitrile-butadiene rubber (NBR), acrylonitrile-butadiene-styrene rubber, natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, ethylene-propylene rubber, ethylene-propylene terpolymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, syndiotactic 1,2-polybutadiene, epichlorohydrin rubber, silicone rubber, polysulfide rubber, polynorbornene rubber, hydrogenated nitrile rubber and the like; and thermoplastic elastomers such as polystyrene elastomer, polyolefin elastomer, polyvinyl chloride elastomer, polyurethane elastomer, polyamide elastomer, polyurea elastomer, polyester resin, fluoric resin and the like.
Alternatively, in a case that the cylindrical member is made of one of the metal and the metal-contained alloy, the elastic layer can be formed of material of at least one selected from a group consisting of polycarbonate resin; a fluoric resin such as ethylene-tetrafluoroethylene (ETFE) and polyvinylidene fluoride (PVDF); styrene resin (homopolymer or copolymer containing styrene or styrene substituent) such as polystyrene, polychlorostyrene, poly-xcex1-methylstyrene, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylate copolymer, styrene-ester methacrylate copolymer, styrene-methyl xcex1-chloroacrylate copolymer, and styrene-acrylonitrile-acrylate copolymer; methyl methacrylate resin; butyl methacrylate resin; ethyl acrylate resin; butyl acrylate resin; modified acrylic resin; vinyl chloride resin; vinyl chloride-vinyl acetate copolymer; rosin modified maleic resin; phenolic resin; epoxy resin; polyester resin; polyester-polyurethane resin; polyethylene; polypropylene; polybutadiene; polyvinylidene chloride; ionomer resin; polyurethane resin; silicone resin; ketone resin; ethylene-ethyl acrylate copolymer; xylene resin; polyvinyl butyral resin; polyamide resin; and modified polyphenylene oxide resin. Also, the elastic layer can be formed of a foam material.
Also, the elastic layer may include a conductive agent to ensure an electric charge on a surface thereof to be smoothly discharged when the photoconductive drum is electrically grounded. The conductive agent can use one among an electrically conductive material made of at least one selected from a group consisting of carbon black, graphite, metal powder such as aluminum and nickel, conductive metal oxide such as tin oxide, titanium oxide, antimony oxide, indium oxide, potassium titanate, antimony tin oxide (ATO), and ITO. The conductive agent may include corpuscles of insulating fine particles made of a material such as barium sulfate, magnesium silicate and calcium carbonate and coated on the electrically conductive material.
The photoconductive drum includes an adhering layer formed between the elastic layer and the photosensitive layer. The adhering layer includes a white pigment and a resin material as a chief ingredient. In this case, the white pigment is made of metal oxide of at least one of titanium oxide, aluminum oxide, zirconium oxide, zinc oxide and the like, and the resin material is made of at least one selected from a group consisting of thermoplastic resin such as ethyl cellulose, polyurethane resin, polyamide resin, polyvinyl alcohol resin, casein, and methyl cellulose; and thermosetting resin such as acrylic resin, phenolic resin, melamine resin, alkyd resin, unsaturated polyester resin and epoxy resin.
According to an aspect of the present invention, there is provided an image forming apparatus including a photoconductive drum forming an image by using an electric potential characteristic of a surface thereof, a charging roller having a rigid body and electrifying the photoconductive drum while pressure-contacting the photoconductive drum, and an image forming part forming a visual image on the photoconductive drum while pressure-contacting the photoconductive drum, and having at least a development roller formed of the rigid body. The photoconductive drum includes a cylindrical member, a photosensitive layer formed on the cylindrical member to be chargeable with electricity, and an elastic layer formed with a thickness greater than 10 xcexcm between the cylindrical member and the photosensitive layer.
In another embodiment of the present invention, a hardness of the elastic layer measured by the Asker xe2x80x9cCxe2x80x9d scale is below 70 degrees.
Also, the image forming apparatus may include an image-transferring part transferring the visual image from the photoconductive drum while pressure-contacting the photoconductive drum, and having at least a transfer roller formed of a rigid body